One relatively new class of engines seeks to utilize two different fuels to gain efficiencies associated with compression ignition combined with advantages associated with burning gaseous fuel such as natural gas. In particular, one type of dual fuel engine utilizes a small pilot injection quantity of liquid diesel fuel that is compression ignited to in turn ignite a much larger charge of natural gas fuel in each engine cylinder. In one strategy for this type of engine, both fuels are directly injected from a single fuel injector associated with each engine cylinder.
For instance, U.S. Pat. No. 7,627,416 appears to teach a dual fuel common rail system in which liquid diesel fuel and natural gas fuel are both injected from a single fuel injector associated with each engine cylinder. This reference recognizes there may be instances in which the engine will need to operate solely on liquid diesel fuel due to exhaustion of the natural gas fuel supply or possibly some fault in the natural gas portion of the system. Certain problems and challenges associated with liquid fuel only operation are neither recognized nor addressed, however.